Spark-type ion source and downstream deflector for mass spectrometer

ABSTRACT

In a mass spectrometer, structure is provided to improve the statistical accuracy of an analytical spectrum especially in that situation where a sample is not homogeneous. The mechanism includes one or both of: (1) structure at the ion source for moving a sample relative to another sample or an electrode of another material; and (2) structure arranged near the ion beam to deflect or suppress the ion beam.

United States Patent Inventor Patrick Powers Binstead, England Appl. No.638,857 Filed May 16,1967 Patented Sept. 7, 1971 Assignee AssociatedElectrical Industries Limited London, Eughnd Priority May 17, 1966, May17, 1966 Great Britain 21825/66 and 21826/66 SPARK-TYPE ION SOURCE ANDDOWNSTREAM DEFLECIOR FOR MASS SPECTROMETER 28 Claims, 6 Drawing Figs.

11.8. CI 250/4L9SA, 250/41.9 SR

Int. Cl H01 j 39/34 Field oiSearch..... 250/41.9 C,

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[56] References Cited UNITED STATES PATENTS 2,690,521 9/1954 Turner250/41.9 X 2,724,056 11/1955 Slepian 250/41.9 2,956,169 10/1960 King eta1 250/41.9 X 3,337,728 8/1967 Friedman et a1 250/41.9

Primary Examiner-William F. Lindquist A!t0rney-Watts, Hoffmann, Fisherand l-leinke ABSTRACT: In a mass spectrometer, structure is provided toimprove the statistical accuracy of an analytical spectrum especially inthat situation where a sample is not homogeneous. The mechanism includesone or both of: (1) structure at the ion source for moving a samplerelative to another sample or an electrode of another material; and (2)structure arranged near the ion beam to deflect or suppress the ionbeam.

PATENTEDSEP mn 3503787 SHEET 2 OF 3 3 INVENTOR.

DATEICK POM/E25 wfm ATTORNEYE SPARK-TYPE ION SOURCE AND DOWNSTREAMDEFLECTOR FOR MASS SPECTROMETER CROSS-REFERENCE TO RELATED APPLICATIONSl. "Present Simultaneous Mass Spectrometer Electrical Outputs, Ser. No.638,287, filed May 16, 1967 by Patrick Powers.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to mass spectrometers and more particularly to a novelapparatus and method of operation of a spark-source mass spectrometer inwhich means is provided for movement of the sample material duringanalysis and in which means is provided for deflecting or suppressing anion beam.

2. Description of the Prior Art With a spark-source mass spectrometer, aspark is drawn either between two sample electrodes or between a sampleand a counter electrode of a metal such as gold to produce ions ofmaterial to be analyzed. In carrying out quantitative analysis by meansof a spark-source mass spectrometer, the statistical accuracy of theresults achieved have, in the past, been very closely associated withthe homogeneity of the sample. This has been true because sparks havebeen drawn from small areas of samples and the ions to be analyzed inthe mass spectrometer are derived from these small areas.

However, the distribution of impurities in many materials, which areanalyzed advantageously in a spark-source mass spectrometer, is nothomogeneous. For this reason, it has been difficult to analyze suchmaterials accurately by mass spectrometry.

When using a spark-source mass spectrometer for the analysis of solids,a photographic plate is normally used as the detector of ions in the ionbeam spectrum. Since the photographic plate acts as an integratingdevice, it records ion intensity as a density which can be independentof the variations in intensity of the ion beam which may result fromirregularities of the spark.

For the purposes of quantitative analysis, a series of exposures isusually made on adjacent strips of the photographic plate, each exposurediffering from the previous one by the same multiplying factor, usuallya factor of 3. In order to compensate for the above-mentioned variationsin intensity, exposures are usually measured in terms of the electricalcharge deposited on the plate, rather than in terms of time. A typicalexposure range is on the order of 0.00001-1,000 millimicrocoulombs. Itis very difficult to arrange for exposures in the lower region of such arange since such small exposures require a small beam current for ashort time. Also, to obtain such exposures, the conditions of the ionsource must be markedly different from what they are normally.

In an attempt to overcome these difficulties, the possibility of movingthe sample during analysis has been explored. Specifically, work hasbeen carried out with moving a pointed electrode relative to a slowlytranslated plane coated with sample material and with moving a pointedelectrode relative to a rapidly rotating plane coated with samplematerial. These proposals have inherent difficulties which include: (1)that of providing a sample in a plane that is uniform; (2) that ofproviding a plane coated with a sample without modifying the chemical orphysical properties of the sample; (3) that of overcoming, with certainmaterials, the problem that there is little, if any, beneficial effecton the homogeneous problem; (4) that of effecting high speed revolutionof a sample in a vacuum; and, (5) that of providing analytical studiesof sufficient length to provide true statistical accuracy.

SUMMARY OF THE INVENTION According to one aspect of the presentinvention, a sparksource for a mass spectrometer is provided forproducing ions of a material to be analyzed, the ions being produced bymeans of a plurality of spark electrodes, at least one of whichcomprises a sample to be analyzed. The ion source is provided with meansfor moving at least one of the electrodes so as to substantiallycontinually change the position of the area on the sample from whichsparks will be drawn and ions produced.

The technique of the present invention increases the area on the samplefrom which ions are taken, compared with known techniques of usingstationary electrodes or with the point-to-plane technique. If, asusually is the case, there are two cylindrical sample electrodesarranged side-by-side, the movement may consist of rotating one or bothof them about its axis, the direction and speed of rotation being chosendependent on the sample material, the size of the exposure being made,or on the spark-source being used which, for example, may be a radiofrequency or DC spark. Alternatively or additionally, the samples may bevibrated relative to one another to increase the area on the sample fromwhich sparks are drawn and ions produced.

In cases where sample rotation is used, variation of the speed and/ordirection of rotation is used to control the sensitivity of analysiswhen necessary. Accordingly, in one instance the two electrodes may berotated in the same direction and in another instance they may berotated in contrary directions. Generally, it is preferred to rotate theelectrodes in a manner such that the portions on the electrodes fromwhich sparks are drawn move toward the ion chamber exit slit of the massspectrometer.

According to another aspect of the present invention, a means foranalyzing substances by mass spectrometry is provided in which theeffective exposure of an integrating ion detector is built up from oneor more successive individual exposures. The succession of individualexposures is terminated when the charge accumulated on the detector hasreached a predetermined value representing the effective exposurerequired. Preferably, the individual exposures are of equalpredetermined duration and time, which must of course be short enough toprovide the minimum effective exposure required with the beam at itsmaximum possible intensity.

Accordingly, a mass spectrometer is provided with a means forintermittently deflecting the ion beam away from an integrating iondetector. The means may comprise a slit through which the beam must passif it is to fall on the ion detector, and accompanying means either forrepeatedly sweeping the beam across the slit, preferably at apredetermined rate of deflection, or means for repeatedly switching thebeam into the slit, preferably for equal predetermined periods of time.Although exposures are normally measured by determining the chargeaccumulated on the ion detector, it is also possible to measure them interms of time and, with the present invention, it is contemplated thatexposures may be measured by determining the number of sweeps the ionbeam makes across the slit.

In order to avoid the necessity for large potentials which might berequired for deflecting the ion beam in this way by means ofconventional deflector slits, and thus to enable transistor circuits tobe employed for this purpose, it is contemplated that a form of theinvention will comprise plates extending alongside the beam path so thatthe beam may be deflected gradually over a considerable distance.

The invention enables short effective exposures of a photographic plateor other integrating ion detector to be achieved while a relativelyintense ion beam is flowing through the mass spectrometer. Thus, theconditions in the ion source can be maintained substantially constantduring a series of such exposures and analysis can be accomplished moreaccurately and more reproducibly. This is particularly advantageous inthe analysis of aluminum and other mono-isotope materials andinhomogeneous specimens.

Accordingly, an object of the present invention is to provide a massspectrometer with a novel apparatus and method whereby relativelyinhomogeneous samples can be analyzed with greater accuracy.

An additional object of the present invention is to provide a novelmethod and apparatus for analyzing substances by mass spectrometry inwhich short exposures of the ion detector can be achieved while normalion source conditions are maintained.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows an ion source somewhatschematically and a sectional view of structure connected to the sourcefor rotating a sample or samples;

FIG. 2 shows an ion source somewhat schematically and an elevationalview with parts broken away and removed for vibrating a sample orsamples;

FIG. 3 is an end elevational view seen from the left side of FIG. 2;

FIG. 4 is an exploded view of deflector plates adjacent the exit of anion source;

FIG. 5 is a schematic view of a spark-source mass spectrometer includingdeflector plates and means for rotating a sample or samples; and,

FIG. 6 is a circuit diagram of the circuit which provides a pulse to oneof the deflector plates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One aspect of the presentinvention shown in FIG. 1 generally comprises structure connected to asample or samples for rotating them in a spark-source type massspectrometer. An ion source is provided and designated generally by thenumeral 10. The ion source 10 includes an enclosure wall 11 defining anionization chamber 12. The rotation structure is designated generally bythe numeral 14. Although only one rotation structure 14 is shown in FIG.1, it is preferred that a second one be provided at a diametricallyopposite position in the enclosure wall 11 for rotating another sampleor counter electrode. Accordingly, a sample or counter electrode 18located adjacent a sample 18 represents either a second sample of thesame material as the sample 18 or may be a counter electrode such as agold electrode. The rotation structure 14 includes a motor 15 coupledthrough a flexible shaft 16 to a sample drive assembly 17. As shown, thedrive assembly 17 is connected to the sample 18 by intermediate memberswhich will be described presently.

The drive assembly 17 includes a mounting flange 20 connected to theenclosure wall 11. A threaded adapter 21 is connected to the mountingflange 20 and is in turn surrounded by a tubular adjusting piece 22 towhich it is threadably connected. As the adjusting piece 22 is rotatedit will move translationally along its axis relative to the adapter 21.At its outer end, the adjusting piece 22 is provided with a bearing ring24 which engages a small projection on a pressure plate 26. The pressureplate 26 does not rotate as the adjusting piece 22 is rotated, but ismoved translationally with the adjusting piece 22.

An adjusting plate 30 is another portion of the drive assembly 17. Theadjusting plate 30 is movable relative to the pressure plate 26 by meansof adjustment micrometers 35, 36. The adjusting plate 30 includes atubular projection 40 which surrounds inner structure of the driveassembly 17. A bearing retention cap 42 is mounted on the end of theprojection 40. The bearing retention cap 42 supports a flexible shaftretention cap 44.

A coupling drive shaft 46 is journaled in the projection 40 by bearings47, 48. The drive shaft 46 is connected to the flexible shaft 16 by endand spline members 49, 50, respectively. The end and spline members 49,50 are held in place by the shaft retention cap 44.

A drive cup 52 is mounted on the inner end of the shaft 46. The drivecup 52 carries a ring magnet 53 which forms a part ofa couplingdesignated generally by the numeral 54.

The ring magnet 53 surrounds another ring magnet 55 mounted on the endofa shaft 60. THe ring magnets 53, 55 are so arranged that rotation ofthe ring magnet 53 causes rotation of the ring magnet 55. The shaft 60is journaled in a flanged mounting tube 62 and is rotatably supported onbearings 64. The bearings 64 are preferably composed ofpolytetrafluoroethylene, referred to hereinafter as PTFE, marketed by E.I. DuPont under the trademark TEFLON.

A flanged portion of the mounting tube 62 is connected to a bellows 65which in turn is connected at its inner end to the mounting flange 20. Acup 66 is mounted on the other side of the flanged portion of themounting tube 62 and a gasket 67 is interposed between them. The gasket67 and the cup 66 are provided to seal off the ionization chamber 12from the outer atmosphere. Cylindrical walls of the cup 66 pass betweenthe magnets 53, 55. The magnets 53, 55 provide a drive coupling which,in conjunction with the cup 66 and associated structure overcomes theproblem of vacuum leaks which could occur with conventional gear ordirect shaft drive assemblies.

The mounting tube 62 carries a nonrotating insulating member 68 whichmay be moved lengthwise within the mounting flange 20 by operation ofthe adjustment plate 22, and fine adjustment laterally and/or lengthwiseis accomplished by operation of the adjustment micrometers 35, 36.Within the insulating member 68, the inner end of the shaft 60 isconnected to a coupling member 69 which is preferably comprised of PTFEfor its insulating properties. The coupling member 69 is in turnconnected to a sample support shaft 72 which is journaled in ballbearings 76, 77 mounted within the insulating member 68 near its innerend. The inner end of the sample support shaft 72 is connected to asample holder 80 which holds the sample 18.

A potential is supplied to the sample 18 through a conductor 82connected to a carbon brush 84. The carbon brush 84 engages a tubularcopper bushing 86 surrounding the shaft 72. The carbon brush 84 isbiased against the copper bushing 86 by a ringlike spring 88. As shown,another sample 18, which may be a counter electrode composed of gold ismounted in a sample holder 80 connected to rotation structure (notshown) which is identical to and arranged opposite the rotationstructure 14. Potential is also supplied to the sample or counterelectrode 18 such that the potential difference between samples 18, 18'is, for example 80 kv. at a frequency of 500 kilocycles.

In operation, rotation is provided by the motor 15 to the drive assembly17 in which magnets 53, 55 coact to provide drive to the shaft 60 andultimately to the sample 18. The sample 18 is similarly caused torotate. Speeds of rotation are typically on the order of -600revolutions per minute, but may be more or less if desired.

Preferably, the samples are cylindrical and are arranged side-by-sidewith their cylindrical surfaces adjacent one another. The desiredspacing between the samples 18, 18 and suitable axial positions relativeto one another may be had by appropriate adjustment of the adjustingplate 22 and/or the adjustment micrometers 35, 36.

With the above-described sample rotation arrangement, the sensitivity ofanalysis may be controlled somewhat by varying the speed and/ordirection of rotation of the samples 18, 18'. For example, the samples18, 18 may be rotated in the same direction or may be rotated inopposite directions, depending upon the particular end result desired.Generally, it is preferred to rotate the samples 18, 18 in oppositedirections so that the portions from which sparks are to be drawn movetoward an exit slit of the ion chamber leading to the analyzer portionof a mass spectrometer.

For reasons which are explained more fully elsewhere in thisspecification, vibration ofa sample enhances the statistical accuracy ofthe results obtained with a mass spectrometer. As will be apparent tothe mechanic skilled in the art, the structure thus far described may beequipped with a mechanism to vibrate the samples. However, the structureshown in FIGS. 2 and 3 is an alternative to the rotation means shown inFIG. 1. In a conventional spark-source type mass spectrometer, there isvariation in a spark as it is drawn between two samples or a sample andcounter electrode. The provision of relative vibration of the samplescontrols this variation and causes the spark to move along the sample toproduce better statistical analysis of the sample.

Referring to FIGS. 2 and 3, the vibration structure comprises a vibratormotor 100 mounted on a bracket 101 and having its output connected nearthe middle of one portion of an elongated L-shaped plate 102. Anadjusting screw 108 is provided to connect the plate 102 to the motor100. Locking nuts 104, 106 maintain the plate 102 in an adjustedposition along the screw 108. The other portion of the plate 102 carriesa pair of spaced fulcrum screws 112 and connects to a rod 115 spacedmidway between the fulcrum screws 112. The fulcrum screws 112 are heldin an adjusted position relative to the plate 102 by means of lockingnuts 116 and shank bushings 117. The plate 102 engages the rod 115 butis permitted a certain degree of movement depending on the adjustedposition of the fulcrum screws 112 which engage a plate 122 mounted onan ion source enclosure wall 11'.

A glass insulator 130, located within the ionization chamber 12',connects to the rod 115. A bellows 131 connects the rod 115 to the plate122 permitting vibrating movement of the rod 115 and the insulator 130relative to the enclosure wall 11'. A sample support 132 is connected atthe inner end of the glass insulator 130. A sample 134 is connected tothe sample support 132. The sample 134 is preferably cylindrical, butmay be of another appropriate configuration.

A similar sample 135 or counter electrode is positioned, for example,substantially parallel to the sample 134. The sample 135 may bestationary or, may also be connected to identical vibration structure(not shown) arranged diametrically opposite the vibration structureshown. Wlth such an arrangement, as the samples are vibrated, the sparkwill be drawn from different surface portions of the samples. Avibration frequency on the order of 50-60 cycles per second has beenfound to be appropriate.

Another aspect of the present invention which may be used advantageouslywith either or both of the above-mentioned improvements generallycomprises an ion beam deflection 'means 136 shown in FIG. 4. A beamdeflection signal circuit 137, shown in FIG. 6, provides a deflectionsignal to the deflection means 136. The deflection means 136 may bepositioned in the ion beam just outside the ion source, and therespective positions of the ion source and the analyzer, or analyzers ifthe device is to be used in a mass spectrometer employing bothelectrostatic and magnetic deflection, is indicated by the arrows. Asshown in FIG. 5, in a double focusing mass spectrometer, an ion source11" produces ions of material which are established by known means as anion beam along a path. The deflection means 136 is mounted near the ionpath in an ion tube 139 between the ion source 11" and the electrostaticanalyzer 140, but may be positioned e1- sewhere in the instrument nearthe ion beam path. An ion tube, not shown, extends through anelectrostatic analyzer 140 to a magnetic analyzer 142 which in turn isconnected to an ion collector means 143 for receiving the ion beam to beanalyzed. A suitable collector means 143 may, for example, be one of thecollector arrangements disclosed in the referenced copending applicationof Patrick Powers.

During analysis, an ion beam, indicated by the dotted line 146, proceedsfrom the ion source 11" toward the analyzer 140 through a hold 150,preferably having a diameter of 0.06 inches, near the center of acircular, conductive plate 152. The plate 152 may have additional holesto accommodate additional ion beams. Spaced from the plate 152 are apair of conductive, substantially semicircular deflection plates 154,155 having flange portions 158, 159 forming a gap 169 preferably of0.125 inches between them. The plate 154 is connected to ground and theplate 155 is connected to the deflection signal circuit 137 via aconductor 161. Another circular, conductive plate 162 is spaced from andcoaxial with the plates 152, 154, 155 and has a hole 163, preferably 0.8inches in diameter, near its center to permit the passage of the ionbeam 146. The plate 162 may be provided with additional holes alignedwith the gap 160 as desired.

The deflection means 136 may be assembled in a mass spectrometer byplacing spacers 167 on the source side of the plate 152 and spacers 168between the plate 152 and the deflection plate 154. The spacers 167, 168are preferably conductive material such as a nickel-chromium alloywhich, for example, may be an item marketed by Driver-Harris Co.,Harrison, New Jersey, under the name NICHROME. Spacers 169 of insulatingmaterial such as quartz are placed between the plate 152 and thedeflection plate 155. Similarly, NICHROME spacers 170 are placed betweenthe deflection plate 154 and the plate 162, and quartz spacers 171 areplaced between the deflection plate 155 and the plate 162. Studsincluding central portions 176 and threaded end portions 178 may beinserted through the appropriate holes in the plates. Suitable nuts andwashers may be fixed to the analyzer ends of the end portions 178, andthe source ends of the end portions 178 may be fixed to structure withinthe ion tube 139. The central portions 176 are preferably composed of asilica material, for example, an item marketed by the Thermal AmericanFixed Quartz Co., Dover, New Jersey, under the name VITREOSIL.

The deflection signal supplied to the deflection plate 155 to cause theion beam 146 to be deflected or suppressed is established in thedeflection signal circuit 137. It is necessary to provide the deflectionsignal circuit 137 since ordinary commercial pulse generators will notprovide a pulse, for example, on the order of +200 volts, which isrequired to deflect or suppress an ion beam including ions having anenergy on the order of 20 kv. the deflection signal is preferably a fastsquare wave whose height is fixed but whose width may be varied. With avariable width pulse, the duration of intermittent ion beam exposuresmay be varied. In addition, means is provided so that a continuousdeflection signal of constant voltage may be supplied to the deflectionplate 155.

Power is supplied to the deflection signal circuit 137 from analternating current source connected to a primary winding 186 of atransformer 187 including secondary windings 188, 189. An output fromthe secondary winding 188 is applied to a full-wave rectifier bridge190. One of the inputs of the rectifier bridge 190 is connected to thesecondary winding 188 via a resistor 192. The rectifier bridge 190 has apositive output terminal 193 connected to a conductor 194 and a negativeoutput terminal 195 connected to a conductor 196 which in turn isconnected to a grounded conductor 197. The output from the secondarywinding 189 is applied to a full-wave rectifier bridge 198. One of theinputs of the rectifier bridge 198 is connected to the secondary winding189 via a resistor 199. The rectifier bridge 198 has a positive outputterminal 199 connected to the conductor 197 and has a negative outputterminal 200 connected to a conductor 201. The positive output terminal199 is also connected via a conductor 202 to ground and to shielding 20on the transformer 187.

A portion of the deflection signal circuit 137 connected across therectifier bridge 190 includes a pair of filer capacitors 205, 206,connected in parallel across the conductors 194, 197. A resistor 208 isinterposed in the conductor 194 between the connections for the filtercapacitors 205, 206. Three Zener diodes 210, 21 1, 212, provided toprotect against surges, are connected in series across the conductors194, 197. A stabilized positive supply voltage of +250 volts withrespect to ground appears across the Zener diodes 210-212.

A portion of the deflection on circuit connected across the rectifierbridge 198 includes a filter capacitor 215 connected across theconductors 197, 201. A Zener diode 219 is also connected across theconductors 197, 201 to protect against surges. A resistor 220 isinterposed in the conductor 201 between the connections for the filtercapacitor 215 and the Zener diode 219. A stabilized negative supplyvoltage of -12 volts, fi percent, appears across the Zener diode 219.

The deflection signal circuit 137 includes a high speed driver stage 230for providing an output to an amplifier 232, which may be referred to asa beanstalk amplifier, which in turn delivers an output pulse to aconductor 234. The output appearing on the conductor 234 is fed to theconductor 161 connected to the deflection plate 155.

An input pulse is provided to the deflection signal circuit 137 along aconductor 236 via a contact C1 of a reed relay 238 shown in its normallydeenergized condition in FIG. 6. The input pulse appearing on theconductor 236 may be provided by an ordinary pulse generator which, forexample, may be a Rutherford type CMCB14, a Data Pulse Model 100, or anyother pulse generator which will provide a variable width pulse ofnegative 14 volts with respect to ground with a rise time of less than30 microseconds.

The input pulse appearing on the conductor 236 is fed via contact C1 tothe high speed driver stage 230 via a conductor 240. The conductor 240is connected via a resistor 242 to base 244 of a PNP transistor 246, onthe one hand, and is connected via a resistor 248 to base 250 of an NPNtransistor 252, on the other hand. Emitter 256 of the transistor 246 isconnected to the conductor 197, and the base 244 of the transistor 246is connected to the conductor 197 via a diode 254. Emitter 260 of thetransistor 252 is connected to the conductor 201, and the base 250 ofthe transistor 252 is connected to the conductor 201 via a diode 258.The diodes 254, 258 are fast switching diodes to provide overvoltageprotection between the base and emitter elements of the associatedtransistors. Collector 262 of the transistor 246 is connected tocollector 264 of the transistor 252 and a conductor 266 via diodes 267,268, 269, and 270.

An output from the driver stage 230 is fed to the amplifier 232 via theconductor 266 connected to base 282 of an NPN transistor 284. A diode286 is connected across the base 282 and emitter 288 of the transistor284. The diode 286 is a fast switching diode to provide overvoltageprotection between the base 282 and the emitter 288. Collector 290 ofthe transistor 284 is connected to emitter 292 of an NPN transistor 294via a conductor 296. The emitter 288 of the transistor 284 is connectedto base 298 of the transistor 294 via a conductor 300 including aresistor 302. The emitter 288 is also connected to the conductor 201 viaa resistor 303. A diode 304 is connected across the conductors 296, 300.The diode 304 is a fast switching diode to provide overvoltageprotection between the base 298 and the emitter 292 of the transistor294. The base 298 is connected via the conductor 300 and a resistor 306to a point on the conductor 194 between two resistors 308, 310. Theresistor 308 is a load resistance and the resistor 310 is provided toinsure adequate base drive current to the transistor 294 in its oncondition. Collector 312 of the transistor 294 is connected to thecathode element of a diode 314 in conductor 197 and to the cathodeelement of a diode 314 in conductor 194. The diodes 312, 3. The may betermed catching diodes" vibrated insure that the output pulse appearingon conductor 234 will fall to zero within plus or minus 0.2 volts. Thisrange is especially important, since the ion beam 146 is switched onwhen the signal appearing on the conductor 234 is in the zero voltagecondition.

In operation, an input pulse is provided to the deflection signalcircuit 137 on the conductor 236 from a pulse generator of the typedescribed. When the input pulse from the pulse generator is at zerovolts, the transistor 246 is turned off; the transistor 252 is turnedon; the transistors 284, 294 are turned off; and, the output voltageappearing on the conductor 234 is a positive 200 volts. When the outputfrom the pulse generator is at a negative 14 volts, the transistor 246is turned on; the transistor 252 is turned off; the transistors 284, 294are turned on; and, the output voltage output on the conductor 234 iszero volts, with respect to ground, plus or minus 0.2 volts.

The output pulse appearing at the conductor 234 during such operationmay be further described as being a square wave having a height of plus200 volts with respect to ground, having rise and fall times of lessthan 200 nanoseconds, and having a variable width of not more than 400nanoseconds longer than the input pulse appearing on the conductor 236from the pulse generator. It should be understood that during periodswhen the deflection signal is at a positive 200 volts, the ion beam 146will be deflected toward the ground plate 154 and in effect, suppressed.

The ion beam 146 may be deflected or suppressed for longer periods oftime by providing a suitable supply signal, which may be referred to asa condition" signal, along a conductor 320 including a resistor 322connected to the relay 238, which is preferably a reed relay. A suitablesupply would produce a signal of 15 volts and 20 milliamperes, whichsupply may be connected to the conductor 320 for as long a period asdesired to deflect or suppress the ion beam 146. When the condition"signal is applied to the conductor 320, the relay 238 is energizedcausing a transfer to relay contact C2 resulting in the base 244 of thetransistor 246 being connected to ground through the resistor 242. Thisturns the transistor 246 off. in this condition, the transistor 252 ison; the transistors 284, 294 are off; and, a positive signal ofapproximately 200 volts appears on the conductor 234 to deflect orsuppress the ion beam 146. It should be understood that as long as thecondition" signal is applied to the conductor 320, that a positiveoutput voltage of approximately 200 volts will appear on the conductor304 to deflect or suppress the ion beam 146.

In one mode of operation, the ion beam 146 may be normally deflectedonto the grounded deflection plate 154 by applying the condition" signalto the conductor 320. When the spark between the samples has reached itsoperating level, the condition pulse may be tenninated, causing atransfer to relay contact C1 to produce a pulsed deflection signal onthe conductor 234. The pulsed deflection signal will intermittently orperiodically deflect the ion beam onto the deflection plate 154 andswitch the ion beam 146 into a path between the gap 160 and through thehole 163 to be ultimately collected. Thus, for effecting a succession ofindividual exposures on the collecting means 143, the deflection plate155 is repeatedly and rapidly brought from its normally positivepotential condition to zero potential and back again to its normallypositive condition of the same polarity. Thus the ion beam 14 is alwaysdeflected in the same direction away from its path toward collectingmeans 143.

Alternatively, the deflection plate 155 could be made alternatelypositive and negative with respect to ground as by applying a sine-waveor other suitably shaped alternating potential to it. With such asignal, the ion beam would be swept across the gap and through the hole163 in both directions.

For terminating a succession of individual exposures when the chargelaid down on the ion detector or collector means has reached apredetermined value representing the effective exposure required, anauxiliary ion collector 145, as shown in FIG. 5, may be provided infront of the collector means 143 (that is, between it and the lastanalyzer stage of the spectrometer). The auxiliary ion collector 145 hasa slit through which about half of the ions will pass to the collectormeans 143 when the beam is in focus. The other half will impinge on theauxiliary collector 145, and the latter is connected to a capacitivestorage circuit C which acts as an integrator of the beam current and isarranged automatically to terminate the succession of exposures, forexample, by operating the relay 238, when a predetermined quantum ofions has been collected and a corresponding quantum of ions has passedto the collector means 143. Systematic errors which might otherwiseresult in inaccurate exposures, such as fluctuations in supply voltageor variations in the spark, can thus be avoided. it should also berecalled that deflection of the ion beam 146 is accomplished whilemaintaining relatively constant conditions in the ion source 11" therebyfurther enhancing the accuracy of analysis.

Many modifications and variations of the invention will be apparent tothose skilled in the art in view of the foregoing detailed disclosure.Therefore, it is to be understood that, within the scope of the appendedclaims, the invention can be practiced otherwise than as specificallyshown and described.

What is claimed is:

1. A mass spectrometer for analyzing material comprising:

a. a spark-type ion source including first and second means to mount apair of electrodes, at least one of which is a sample electrode, inspaced relationship and means for drawing a spark between the electrodesfor producing ions of a material to by analyzed, the ions beingestablished as an ion beam along a path;

. one of the mounting means including means for rotating the sampleelectrode;

. the first mounting means including means for vibrating its supportedelectrode relative to the other electrode while maintaining the two inspaced relationship;

. a magnetic analyzer disposed along the ion beam path;

. collector means disposed in the ion beam path for receiving ions to beanalyzed; and deflection means disposed adjacent the ion beam path fordeflecting the ion beam so as to interrupt exposure of the ion beam onsaid collector means.

2. The apparatus of claim 1 wherein a deflection signal circuit forproducing a pulsed deflection signal is connected to the deflectionmeans.

3. The mass spectrometer of claim 1 wherein the vibrated electrode is asample.

4. The mass spectrometer of claim 1 wherein both electrodes are rotated.

5. A mass spectrometer for analyzing material comprising:

a. a pair of electrodes, at least one of which is a cylindrical sampleelectrode, said electrodes being generally parallel and in side-by-siderelation;

b. a spark-type ion source including means to mount the electrodes inspaced relationship and draw a spark therebetween to produce ions of amaterial to be analyzed, the source also including means to establishthe ions as an ion beam along a path;

c. the one of the mounting means supporting the sample electrodeincluding means for rotating the sample electrode to increase the areaof the sample from which the spark is drawn by drawing the spark overthe annular surface portion of the specimen while restraining the sampleelectrode to prevent movement along its axis;

d. a magnetic analyzer disposed along the ion beam path;

and,

e. collector means disposed in the ion beam path for receiving ions tobe analyzed.

6. The mass spectrometer of claim 5 wherein each mounting means includesmeans for rotating its supported electrode.

7. The mass spectrometer of claim 6, wherein the means for rotating thesupported electrodes rotate the electrodes in opposite directions suchthat the portions of the electrodes from which a spark is drawn movetoward an ion chamber exit in the direction of ion beam travel.

8. A mass spectrometer for analyzing material comprising:

a. a pair of electrodes, at least one of which is a cylindrical sampleelectrode, said electrodes being generally parallel and in side-by-siderelation;

b. a spark-typeion source including means to mount the electrodes inspaced relationship and draw a spark therebetween to produce ions of amaterial to be analyzed, the source also including means to establishthe ions as an ion beam along a path;

. one of the mounting means including means to vibrate its supportedelectrode substantially constantly to increase the area of the samplefrom which the spark is drawn by drawing the spark over the surface ofthe sample of electrode as a spark is drawn toward and away from theother electrode while maintaining the electrodes in spaced relationship;

d. a magnetic analyzer disposed along the ion beam path;

and,

e. collector means disposed in the ion beam path for receiving ions tobe analyzed.

9. The mass spectrometer of claim 8 wherein each of the mounting meansincludes means to vibrate its supported electrode while maintaining theelectrodes in spaced relationship.

10. The method of analyzing material in a mass spectrometer comprisingthe steps of:

ill

a. producing ions of the material to be analyzed by drawing; a sparkbetween first and second electrodes one of which. is a sample electrode;b. rotating the sample electrode as the spark is being drawn; c.vibrating at least the first electrode as the spark is being.

drawn while maintaining the electrodes in spaced relationship;

d. establishing the ions in an ion beam;

e. deflecting the ion beam with a magnetic analyzer; and,

f. collecting the ion beam on a collector and intermittentlyinterrupting the collection of the ion beam on the collector bydeflecting the ion beam.

11. The method of claim 10 wherein intermittently deflecting the ionbeam is accomplished by applying a pulsed deflec- 1 tion signal todeflection plates arranged near the ion beam.

12. The method of analyzing the material in a mass spectrometercomprising the steps of:

a. producing ions of the material to be analyzed by drawing a sparkbetween electrodes, at least one of which is a sample, said electrodesbeing generally parallel and in sideby-side relation;

b. vibrating at least one electrode during the period of the spark whilemaintaining the electrodes spaced, thereby increasing the area of thesample from which the spark is drawn by moving the spark along theelectrodes to produce ions from a relatively large sample surface area;

c. establishing the ions in an ion beam;

d. deflecting the ion beam with a magnetic analyzer; and,

e. collecting the ion beam on a collector.

13. The method of claim 12 wherein both electrodes are vibrated as theyare maintained in spaced relationship.

14. The method of analyzing material in a mass spectrometer comprisingthe steps of:

a. producing ions of the material to be analyzed by drawing a sparkbetween electrodes, at least one of which is a sample electrode, saidelectrodes being generally parallel and in side-by-side relation; and,

b. distributing the ion production over an annular surface of the sampleelectrode thereby increasing the area of the sample from which the sparkis drawn by rotating the sample electrode as the spark is being drawn.while restraining the sample electrode to prevent movement along itsaxis.

15. The method of claim 14, wherein both electrodes are rotatedsimultaneously.

16. The method of claim 15, wherein the electrodes are rotated inopposite directions such that portions of the electrodes from which aspark is drawn are moved toward the path of ion travel.

17. A method of analyzing material in a mass spectrometer comprising thesteps of:

a. producing ions of the material to be analyzed by drawing a sparkbetween electrodes at least one of which is a sample;

b. establishing the ions in an ion beam;

c. deflecting the ion beam with a magnetic analyzer;

d. collecting the ion beam on a collector; and,

e. extending the time over which ions are collected and therebyobtaining a more reliable spectra of the sample by intermittentlyinterrupting the collection of the ion beam on the collector bydeflecting the ion beam.

18. The method of claim 17, wherein intermittently deflecting the ionbeam is accomplished by applying a pulsed deflection signal todeflection plates arranged near the ion beam.

19. The method of analyzing the material in a mass spectrometercomprising the steps of: I

a. producing ions of the material to be analyzed by drawing a sparkbetween electrodes, at least one of which is a sample;

b. vibrating at least one electrode during the period of the spark whilemaintaining the electrodes spaced, thereby moving the spark along theelectrodes to produce ions from a relatively large sample surface area;

c. establishing the ions in an ion beam;

d. deflecting the ion beam with a magnetic analyzer;

e. collecting the ion beam on a collector; and,

f. intermittently deflecting the ion beam so as to interrupt collectingthe ion beam on the collector means.

20. In a mass spectrometer having an ion source, a collector, structureestablishing a path of travel of an ion beam from said ion source tosaid collector, and an analyzer along said path of travel for deflectingsaid beam and focusing portions of said beam onto said collector, theimprovement comprising:

a. deflection means disposed adjacent said path of travel for deflectingsaid ion beam; and

b. energizing means for energizing said deflection means with signals ofpredetermined width to interrupt focusing of said beam on said collectorcyclically during analysis of a given sample to increase reliability ofsaid analysis.

21. The improvement of claim 20, wherein said width is variable.

22. The improvement of claim 20, wherein said deflection means comprisesa pair of spaced apart conductive plates defining a gap through whichsaid ion beam passes when said deflection means are unenergized 23. Theimprovement of claim 22, wherein one of said plates is maintained at aconstant potential and the other of said plates is connected to saidenergizing means.

24. The improvement of claim 23, wherein said constant potential isground potential.

25. The improvement of claim 24, wherein said energizing means providespositive signals to prevent said ion beam from passing through said gap.I

26. The improvement of claim 25, wherein said width is variable.

27. A method of analyzing material in a mass spectrometer, whichmaterial may have impurities therein, comprising the steps of:

a. producing ions of the material to be analyzed;

b. establishing the ions in an ion beam;

c. deflecting the beam with an analyzer;

d. collecting the ion beam on a collector; and

e. extending the time over which ions are collected and thereby reducingthe effect of said impurities to obtain a more reliable spectra of saidmaterial by interrupting collection of said beam on said collector bycyclically deflecting said ion beam away from said collector duringanalysis of said material.

28. The method of claim 27, wherein the collection of the beam isinterrupted by providing a substantially square wave of variable widthto deflect said beam.

Column Column Column Column Column subst Column Coltunn Column ColumnColumn Column Column (SEAL) Attes't:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 07527 Dated September- 1 197 Invent0r(s) Patrick Powers 6, line itute 6,line line line

line

, line line , line It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

substitute 160 after "output terminal" delete "199",

delete "199", substitute 199a after "shielding" delete "20", substitutedelete "filer", substitute filter delete "on substitute signal delete"3. The", substitute 314,

delete "vibrated" substitute to delete "l4", substitute 146 Signed andsealed this 18th day of April 1972.

EDWARD M.FLETCHJ:JR,JR. Attestinrr Officer ROBERT GOTTSCHALK RM PO1OSO(10-69) USCOMM-DC 603764- 59 w u s, GDVERNMENY Pnm'rmc OFFICE 1909O-JGl-JJI

1. A mass spectrometer for analyzing material comprising: a. aspark-type ion source including first and second means to mount a pairof electrodes, at least one of which is a sample electrode, in spacedrelationship and means for drawing a spark between the electrodes forproducing ions of a material to by analyzed, the ions being establishedas an ion beam along a path; b. one of the mounting means includingmeans for rotating the sample electrode; c. the first mounting meansincluding means for vibrating its supported electrode relative to theother electrode while maintaining the two in spaced relationship; d. amagnetic analyzer disposed along the ion beam path; e. collector meansdisposed in the ion beam path for receiving ions to be analyzed; and f.deflection means disposed adjacent the ion beam path for deflecting theion beam so as to interrupt exposure of the ion beam on said collectormeans.
 2. The apparatus of claim 1 wherein a deflection signal circuitfor producing a pulsed deflection signal is connected to the deflectionmeans.
 3. The mass spectrometer of claim 1 wherein the vibratedelectrode is a sample.
 4. The mass spectrometer of claim 1 wherein bothelectrodes are rotated.
 5. A mass spectrometer for analyzing materialcomprising: a. a pair of electrodes, at least one of which is acylindrical sample electrode, said electrodes being generally paralleland in side-by-Side relation; b. a spark-type ion source including meansto mount the electrodes in spaced relationship and draw a sparktherebetween to produce ions of a material to be analyzed, the sourcealso including means to establish the ions as an ion beam along a path;c. the one of the mounting means supporting the sample electrodeincluding means for rotating the sample electrode to increase the areaof the sample from which the spark is drawn by drawing the spark overthe annular surface portion of the specimen while restraining the sampleelectrode to prevent movement along its axis; d. a magnetic analyzerdisposed along the ion beam path; and, e. collector means disposed inthe ion beam path for receiving ions to be analyzed.
 6. The massspectrometer of claim 5 wherein each mounting means includes means forrotating its supported electrode.
 7. The mass spectrometer of claim 6,wherein the means for rotating the supported electrodes rotate theelectrodes in opposite directions such that the portions of theelectrodes from which a spark is drawn move toward an ion chamber exitin the direction of ion beam travel.
 8. A mass spectrometer foranalyzing material comprising: a. a pair of electrodes, at least one ofwhich is a cylindrical sample electrode, said electrodes being generallyparallel and in side-by-side relation; b. a spark-type ion sourceincluding means to mount the electrodes in spaced relationship and drawa spark therebetween to produce ions of a material to be analyzed, thesource also including means to establish the ions as an ion beam along apath; c. one of the mounting means including means to vibrate itssupported electrode substantially constantly to increase the area of thesample from which the spark is drawn by drawing the spark over thesurface of the sample of electrode as a spark is drawn toward and awayfrom the other electrode while maintaining the electrodes in spacedrelationship; d. a magnetic analyzer disposed along the ion beam path;and, e. collector means disposed in the ion beam path for receiving ionsto be analyzed.
 9. The mass spectrometer of claim 8 wherein each of themounting means includes means to vibrate its supported electrode whilemaintaining the electrodes in spaced relationship.
 10. The method ofanalyzing material in a mass spectrometer comprising the steps of: a.producing ions of the material to be analyzed by drawing a spark betweenfirst and second electrodes one of which is a sample electrode; b.rotating the sample electrode as the spark is being drawn; c. vibratingat least the first electrode as the spark is being drawn whilemaintaining the electrodes in spaced relationship; d. establishing theions in an ion beam; e. deflecting the ion beam with a magneticanalyzer; and, f. collecting the ion beam on a collector andintermittently interrupting the collection of the ion beam on thecollector by deflecting the ion beam.
 11. The method of claim 10 whereinintermittently deflecting the ion beam is accomplished by applying apulsed deflection signal to deflection plates arranged near the ionbeam.
 12. The method of analyzing the material in a mass spectrometercomprising the steps of: a. producing ions of the material to beanalyzed by drawing a spark between electrodes, at least one of which isa sample, said electrodes being generally parallel and in side-by-siderelation; b. vibrating at least one electrode during the period of thespark while maintaining the electrodes spaced, thereby increasing thearea of the sample from which the spark is drawn by moving the sparkalong the electrodes to produce ions from a relatively large samplesurface area; c. establishing the ions in an ion beam; d. deflecting theion beam with a magnetic analyzer; and, e. collecting the ion beam on acollector.
 13. The method of claim 12 wherein both electrodes arevibrated as they are maintained in spaced relationship.
 14. The methodof analyzing material in a mass spectrometer comprising the steps of: a.producing ions of the material to be analyzed by drawing a spark betweenelectrodes, at least one of which is a sample electrode, said electrodesbeing generally parallel and in side-by-side relation; and, b.distributing the ion production over an annular surface of the sampleelectrode thereby increasing the area of the sample from which the sparkis drawn by rotating the sample electrode as the spark is being drawnwhile restraining the sample electrode to prevent movement along itsaxis.
 15. The method of claim 14, wherein both electrodes are rotatedsimultaneously.
 16. The method of claim 15, wherein the electrodes arerotated in opposite directions such that portions of the electrodes fromwhich a spark is drawn are moved toward the path of ion travel.
 17. Amethod of analyzing material in a mass spectrometer comprising the stepsof: a. producing ions of the material to be analyzed by drawing a sparkbetween electrodes at least one of which is a sample; b. establishingthe ions in an ion beam; c. deflecting the ion beam with a magneticanalyzer; d. collecting the ion beam on a collector; and, e. extendingthe time over which ions are collected and thereby obtaining a morereliable spectra of the sample by intermittently interrupting thecollection of the ion beam on the collector by deflecting the ion beam.18. The method of claim 17, wherein intermittently deflecting the ionbeam is accomplished by applying a pulsed deflection signal todeflection plates arranged near the ion beam.
 19. The method ofanalyzing the material in a mass spectrometer comprising the steps of:a. producing ions of the material to be analyzed by drawing a sparkbetween electrodes, at least one of which is a sample; b. vibrating atleast one electrode during the period of the spark while maintaining theelectrodes spaced, thereby moving the spark along the electrodes toproduce ions from a relatively large sample surface area; c.establishing the ions in an ion beam; d. deflecting the ion beam with amagnetic analyzer; e. collecting the ion beam on a collector; and, f.intermittently deflecting the ion beam so as to interrupt collecting theion beam on the collector means.
 20. In a mass spectrometer having anion source, a collector, structure establishing a path of travel of anion beam from said ion source to said collector, and an analyzer alongsaid path of travel for deflecting said beam and focusing portions ofsaid beam onto said collector, the improvement comprising: a. deflectionmeans disposed adjacent said path of travel for deflecting said ionbeam; and b. energizing means for energizing said deflection means withsignals of predetermined width to interrupt focusing of said beam onsaid collector cyclically during analysis of a given sample to increasereliability of said analysis.
 21. The improvement of claim 20, whereinsaid width is variable.
 22. The improvement of claim 20, wherein saiddeflection means comprises a pair of spaced apart conductive platesdefining a gap through which said ion beam passes when said deflectionmeans are unenergized
 23. The improvement of claim 22, wherein one ofsaid plates is maintained at a constant potential and the other of saidplates is connected to said energizing means.
 24. The improvement ofclaim 23, wherein said constant potential is ground potential.
 25. Theimprovement of claim 24, wherein said energizing means provides positivesignals to prevent said ion beam from passing through said gap.
 26. Theimprovement of claim 25, wherein said width is variable.
 27. A method ofanalyzing material in a mass spectrometer, which material may haveimpurities therein, comprising the steps of: a. producing ions of thematerial to be analyzed; b. establishing the ions in an ion beam; c.deflecting the beam with an analyzer; d. colLecting the ion beam on acollector; and e. extending the time over which ions are collected andthereby reducing the effect of said impurities to obtain a more reliablespectra of said material by interrupting collection of said beam on saidcollector by cyclically deflecting said ion beam away from saidcollector during analysis of said material.
 28. The method of claim 27,wherein the collection of the beam is interrupted by providing asubstantially square wave of variable width to deflect said beam.